Study of temperature-sensitive gel electrolytes for energy storage devices with self-protection behavior

The lifetime and application of electrochemical storage devices are always threatened by thermal runaway. Intelligent self-protecting gel electrolytes can be designed using temperature-responsive polymers. However, the mechanisms and factors affecting protective behavior are unclear. Here, we fabricated supercapacitors using temperature-responsive polyacrylamide-2-hydroxyethyl acrylate (PNIPAM-co-HEA) hydrogel polyelectrolytes. It was found that the polymer changed from hydrophilic to hydrophobic with increasing temperature, and the physical cross-linking of the polymer molecular strands in the electrolyte was enhanced, thus restricting conductive ion migration and closing the ion transportation pathway. The hydrophilic–hydrophobic transition on the gel surface also contributed to the suppression of the specific capacitance of the supercapacitor. This self-protection feature is repeatable. In addition, we investigated the effect of methyl groups in the main chain structure on the electrochemical properties using poly( N -isopropylacrylamide-co-2-hydroxyethyl methacrylate) (PNIPAM-co-HEMA). Methylene enhanced the hydrophobicity of the polymer at room temperature and reduced the thermo-protective effect. The methyl group in the main chain also reduced the thermal response temperature of the polymer. This study explores the mechanism by which temperature-responsive polymers inhibit thermal runaway in supercapacitors and provides support for the design of more rational and efficient temperature-sensitive electrolytes.